Operating magnets suppliable with electric current are readily available on the market in a number of embodiments. By way of example, DE 10 2004 017 089 B4 is representative of the pertinent operating equipment, particularly in the form of a proportional double solenoid. This known solution is used in the operation of valves, with at least two windings on one coil former in each case. The coil windings are arranged in each case between two ring flanges at least partially encasing a pole tube by an anchor part being guided movably. The anchor part undergoes transition into a pole core at its one end via a magnetic separation. In the pole core, an operating plunger is guided as an operating part. At its other end, the anchor part at least partially engages a closing part via another magnetic separation. A disk-shaped pole plate is arranged between the adjacent and opposing coil formers. In the known solution, the pole core, the pole tube, as well as the magnetic separations and the closing part form an assembly, onto which the respective coil former with its coil windings and the pole plate can be slipped as another assembly. To always have a defined securing position, at least one of the facing ring flanges adjacent to one another has a projecting component. The projecting component can be engaged with a corresponding recess in the ring flange of the other coil former. As already mentioned above, such operating magnets are used primarily to control hydraulic valves. However, new technical areas are increasingly opening up for which respective operating magnets can be used advantageously.
Subsequently published DE 10 2005 056 816 shows an unlatching device using an operating magnet for emergency activation of a headrest for a motor vehicle seat. In the event the motor vehicle crashes, the headrest moves forward to reduce the free impact surface between the back of the seat user's head and the impact area of the head on the headrest. To control the unlatching of the headrest, a corresponding control part can be moved along a first axis. In an operating position, that control part enables a swing distance extending crosswise to the first axis for a control device arranged to pivot around a second axis. The respective control device also has a locking part that can be unlatched by the operating part of the magnet via the control device. The pathway for the control part to be triggered then releases in the forward direction for an activation process of the headrest.
The problem common to all operating magnets with their coil windings is that in the event of fault currents, overheating caused by overstraining the magnet, etc., can result in fire. Plastic materials used increasingly for weight and practicality reasons for at least one portion of the components of the operating magnet can be easily scorched or can even burn. That risk increases starting from the electrical coil winding via the plastic parts. A fire has a detrimental effect on other connected components of the technical system, such as valves, headrests, etc. Currently both the housing parts of the operating magnet and their encapsulation are made of plastic. Other relevant plastic parts are the coil formers for receiving the coil winding and the plastic insulating layers for the wire winding fitted to the coil former, usually designed in the form of copper wire.
Preferably, the copper wire, as a coated electric wire, is encased over its entire length with a plastic coated insulation to have an electric decoupling between the winding layers in the winding. However, the plastic coated insulation is very heat-sensitive, easily scorches through, and thus forms an ideal fire source. To counteract this fire risk in practice, an electric safety device is installed within the electric supply cycle of the coil winding, primarily in the form of a fuse that is to activate, i.e., is to break, the electric circuit as soon as a short-circuit occurs because of scorched parts of the coating insulation. In practice, the cases show that this electric safety device is not sufficient to effectively counteract the potential fire risk. Thus, cases exist in which the fuse indeed activated and nevertheless a (scorching) fire resulted because of a short-circuit, starting from the operating magnet that was used.